Passenger boarding bridges, as bridges connecting the airport terminals with the aircrafts, provide safe and comfortable space for passengers who walk in and out of the airports, and have been widely used in the airports. Currently, most of the passenger boarding bridges can dock with the aircrafts having the doors to be opened leftwards or rightwards. However, the existing regional aircrafts have the doors designed to be opened downwards and having side rails, i.e., being of the aircrafts having the doors to be opened downwards. Therefore, in the countries and regions where the regional aircrafts are in the majority, the existing cab of the passenger boarding bridge, which is designed for the aircrafts having the doors to be opened leftwards or rightwards, will interferes with the aircraft door when serves the aircraft having the door to be opened downwards, and cannot serve this kind of aircrafts, and accordingly cannot meet the requirements for docking between the regional aircrafts and the passenger boarding bridges.